I use MX16 and want to create a very small ISO - File for old computers. So I uninstalled big tools like LbreOffice, GimP and so on (by using Synaptic and also autoremove). Packages are no longer listed in Synaptic. But when I create an ISO - file by using Snappshot, it takes also 1,2 Gb, as much as the complete MX - Installation needed. What did i wrong?

If you want a smaller .iso, you should look into antiX, where the distro is smaller to start, is made for older machines, and is offered in several flavors to enable smaller custom versions, like the antiX base, where you start minimal, and add just what you need.

"At the moment antiX-17 “Heather Heyer” comes as a full distro (c800MB), a base distro (c620MB), a core distro (c310MB) and a net distro (c150MB) for 32 bit and 64 bit computers. For those who wish to have total control over the install, use antiX-core or antiX-net and build up. Note that the net version will need an ethernet connection."

Did you think of removing unwanted locales and support files. If you're intending to redistributing it to any and all, then removing the locales is not a smart option, but if you intend to use it as a personal tool, then go ahead and remove the locales and their support files, it should make a nice little difference and punitive old CPUs will certainly appreciate it.

When a punitive old CPU tries to expand a highly compressed ISO, it can actually take longer than an ISO with less compression. Last week at work, the bosses old laptop failed to read the HDD on bootup, I was asked to have a look so I used my MX17.1 personalised ISO with max compression on a Core2 Duo laptop with 2GB RAM and chipset graphics. It took a full 3 minutes before I could use the mouse on the desktop. I'm used to times like 15-20 seconds from cold boot.

Thank you for the answers! I use MX to recycle old computers for social projects and so on. To create a reference - system therefor I use a computer without any user files. I used bleachbit and autoremove, but there is nothing to remove. So I wonder, that ISO - file doesnt became smaler after removing great tools (with purge).
But this is not a great problem. Perhaps I will use antiX for very old computers (the look and feel of antiX is not so great) and otherwise I will use also a big ISO.

The size of the ISO is nowhere near as important as the running OS's active memory footprint, which we all know, MX does significantly better than Windows did. With the added benefit Linux is less prone to the malware types Windows is subject to, so has less need of real-time active antivirus to slow it down, so whether you use AntiX or MX, you win.

as a prerequisite step:
issue the command "sudo dpkg-reconfigure locales"
and in the dialog UI, ensure only the locales you are interested in are ticked.

Afterward, launch bleachbit(AsRoot) and tick "localizations" ~~ tick no other line item (not autoremove, nothing else).
The first time you attempt to delete localizations, a bleachbit dialog will prompt you "need to setup via preferenceces".
When you visit bleachbit preferences } localizations, you should find that only english (or whatever) is already marked, so just click OK and close the dialog. The act of visiting the dialog, then closing it, toggles off the "first-run" reminder prompt. Click the Delete button (or the dry-run button first, if you wish) and bleachbit right-pane will tally the localization files slated for removal. You can (should) expect bleachbit will find/remove 22,000+ localization files, occupying approx 500MB on disk. You can (should) also expect the compressed ISO file will be 90 to 110MB smaller. The statement "can expect" is based on reports from multiple testers who have participated in previous tests, across various discussion threads.

which will leave my local LANG and default en_US enabled. By this bleachbit only has my LANG and en_US enabled anyway and will happily remove about 400 MB compresses localization files.
EDIT: Just a cosmetic fix: removed trailing " p;" in the sed-script to avoid dublicate disabled locales.